Embodiments of the present inventive concept provide methods of fabricating semiconductor devices. More particularly, embodiments of the inventive concept provide relatively simplified methods of semiconductor device fabrication during which certain conventional drawbacks associated with polishing steps, (e.g., such as those used during a damascene process or contact formation process) are addressed.
So called phase change memory devices are among a collection of next-generation semiconductor memory devices replacing more conventional memory devices such as DRAMs and flash memories. A phase change memory device includes a plurality of phase change memory cells incorporating one or more phase-change material layer(s). Such phase-change material layer(s) exhibit a variable resistance according to their material state (e.g., a crystalline state verses an amorphous state). Using this property, the phase change memory cells may be programmed by applying certain heating profiles (e.g., passing a defined current for a defined period of time) to the phase-change material layer(s).
As ever, there is great commercial pressure to increase the fabrication density of phase change memory cells. Accordingly, design rules for contemporary phase change memory devices are constantly being reduced, and related fabrication pattern formation processes have migrated from photolithography processes to damascene processes. Due to these trends, the fabrication of phase change memory devices involves the processing of phase change material layers (or phase change material patterns) using a damascene process. For example, a trench of a mold oxide layer may be filled with a phase change material and then subjected to Chemical Mechanical Polishing (CMP) process(es) to form the phase change material pattern into separate nodes associated with respective unit memory cells.
Unfortunately, the fabrication processing of phase change material patterns using CMP process(es) poses several problems. First, a CMP process applied to a phase change material pattern may yield resultant structures having heights (i.e., respective upper surfaces above a substrate or other reference surface structure) that vary according to location of the wafer being processed. Indeed, differing heights for respective portions of a phase change material pattern may arise over the surface area of a single semiconductor memory chip. The fabrication of a phase change material pattern having different heights (and therefore different material thicknesses) results in different current levels (e.g., different reset current Ireset) being passed through respective phase change memory cells.
Additionally, conventional CMP processing often results in a phase change material pattern having an upper surface that is recessed in relation to a surrounding mold oxide layer. In this context, the term “recessed” means a localized concavity or depression in the upper surface of the phase change material pattern relative to the flat surface of surrounding material layer(s). The resulting recessed surface of the phase change material layer pattern has adverse consequences during later-applied fabrication processes. For example, when an electrode is formed on a recessed phase change material pattern, the electrode will have a curved shape, and this unintended curvature in shape may result in cracking of the material layer forming the electrode. Consequently, where a contact is subsequently formed on the electrode, the electrode and/or the phase change material pattern portions of the contact may be damaged.
Additionally, phase change memory devices routinely include certain contacts configured to connect an active region of a semiconductor substrate or material layer to an overlying metal layer (e.g., a wiring layer). Such contacts are formed by a conductive material layer pattern filling a contact hole formed through an interlayer insulation layer. This conductive material layer (e.g., one or more metals) is subjected to CMP processing in a manner similar to that described above with the attendant problems.